Generally, in packet communications between a base station and user equipments in a wireless mobile communications system, the base station schedules uplink packet transmissions for the user equipments. In particular, when user equipments transmits uplink packet to a base station, the base station decides portions and types of resources (time, code, frequency, transmission power, etc.) for entire uplink packet transmissions to be used by a specific user equipment in transmitting a certain volume of data at a specific timing point by considering transmission buffer states and service priorities of user equipments belonging to the base station and an uplink channel status of a user equipment to be scheduled and the like overall. The base station then informs the specific user equipment of the decision via a scheduling command. Subsequently, the user equipment having received the scheduling command performs the uplink packet transmission according to the corresponding command. In this manner, the base station is able to enhance uplink packet transmission efficiency better than that in case of absence of base station scheduling by quickly and appropriately adjusting resource allocation for uplink packet transmissions of the user equipments belonging to the corresponding base station.
In a cellular wireless communications system, when a user equipment is located in the vicinity of a boundary of a cell covered by a base station (or sector) with which packet transmission/reception is performed, considerable quantity of power is required for the packet transmission/reception. So, there exist considerable amount of transmission power losses of the base station and user equipment. Moreover, interference with neighbor cells considerably grows due to the packet transmissions of large transmission power between the base station and the user equipment. To reduce such a bad influence, the user equipment located in the vicinity of the cell boundary is allowed to perform packet transmissions/receptions with a plurality of cells existing in an area capable of covering the corresponding user equipment as well as one cell, which is called soft handover.
FIG. 1 is a diagram to explain a soft handover method according a related art.
Referring to FIG. 1, while a user equipment is in a soft handover state with a plurality of base stations in uplink, if the user equipment performs a packet transmission in uplink, each of the base stations (or sectors) with which the user equipment is in the soft handover state receives the transmitted packet, decodes the received packet and then transmits the decoded data to a central control station via a wire network. The central control station collects data free from reception error from the received data and then transfers the collected data to a data network. In this case, the central control station can be an entity such as a specific base station (or sector) among the base stations (or sectors) in soft handover, a radio network controller (RNC) existing separate from base stations. So, even if the packet reception succeeds in one of a plurality of cells, data of the corresponding packet is correctly transferred to the data network. Compared to a case of a packet transmission to one cell from a user equipment, this case is able to bring the same transmission efficiency with less transmission power.
Meanwhile, a scheduling cell, which schedules a user equipment, should perform scheduling to enable the specific user equipment to retransmit an uplink packet at a next timing in case of failing to receive the uplink packet transmitted by the specific user equipment or to consider retransmission of an uplink packet having been transmitted by the user equipment. However, in case that the specific user equipment is in handover with a different cell as well as the scheduling cell in uplink, once the different cell having succeeded in receiving the packet transmits an ACK signal to the specific user equipment, the specific user equipment may not retransmit the corresponding packet to the scheduling cell. In this case, if the scheduling cell empties uplink resources (uplink power, frequency-time resource, etc.) by expecting the retransmission of the corresponding packet, the uplink resources are wasted and the scheduling becomes inefficient.